Yuanzhi Li

Tuning the Relative Concentration Ratio of Bulk Defects to Surface Defects in TiO2 Nanocrystals Leads to High Photocatalytic Efficiency

TiO(2) nanocrystals with tunable bulk/surface defects were synthesized and characterized with TEM, XRD, BET, positron annihilation, and photocurrent measurements. The effect of defects on photocatalytic activity was studied. It was found for the first time that decreasing the relative concentration ratio of bulk defects to surface defects in TiO(2) nanocrystals could significantly improve the separation efficiency of photogenerated electrons and holes, thus significantly enhancing the photocatalytic efficiency.

Formation of AgI/TiO2 nanocomposite leads to excellent thermochromic reversibility and photostability

AgI/TiO2 nanocomposite was prepared and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and diffusive reflectance UV-vis (DRUV-vis) absorption spectra at different temperatures. The AgI/TiO2 nanocomposite exhibits thermochromic switching phenomena at the phase β–α transition temperature of AgI with the evolution of its color from light yellow at ambient temperature to dark khaki at 150 °C. It was found for the first time that the formation of the AgI/TiO2 nanocomposite not only results in a considerable reduction of thermochromic transition temperature of AgI as well as excellent thermochromic reversibility, but also leads to excellent photostability under illumination with an indoor fluorescent lamp. Based on the characterization results by photoluminescence, transient photocurrent decay and positron annihilation spectra, it is concluded that large surface defects, such as I− vacancy clusters (e.g.Ag+–I−V–Ag+–I−V–Ag+) on the surface of AgI as deep electron traps, are responsible for the photodecomposition of pure AgI. The excellent photostability of the AgI/TiO2 nanocomposite is due to the following reason: the surface I− vacancy clusters as deep electron traps in pure AgI are replaced by Ag+–O2−–Ti4+ bonds on the interface of AgI/TiO2, thus Agncluster formation through the surface migration of photogenerated Ag atoms is completely inhibited, resulting in the inhibition of photodecomposition of AgI.

Highly selective photocatalytic and sensing properties of 2D-ordered dome films of nano titania and nano Ag2+ doped titania

Novel 2D-ordered dome films of nano titania (2D-TiO2) and nano Ag2+ doped titania (2D-Ag-TiO2) were prepared by RF magnetron sputtering method. The existence of oxygen vacancies or Ti3+ ions in the 2D-ordered dome films extends the absorption of TiO2 from UV region to visible region up to 530 nm. Doping of Ag2+ in the 2D-TiO2 film considerably enhance the visible light absorption of the 2D-Ag-TiO2 film. Remarkably, for the photodegradation of cationic crystal violet (CV) and anionic methyl orange (MO), the 2D-ordered dome films exhibit 100% photodegradation selectivity to cationic CV. The 2D-Ag-TiO2 film shows excellent selective photocatalytic durability and photostability without detectable photoreduction of Ag2+ ions after long time illumination. Furthermore, the 2D-ordered dome films exhibit unique ratiometric photoelectrochemical sensing property with 100% selectivity to the cationic CV. Ag2+ doping in the 2D-TiO2 film significantly improves the photocatalytic activity and photoelectrochemical sensitivity as it considerably enhances the charge transfer efficiency from excited dye to titania.

Ultralow density, hollow silica foams produced through interfacial reaction and their exceptional properties for environmental and energy applications†

We report a novel, facile, and reproducible method for large-scale production of highly porous, hollow silica foams (hollow spheres) with a robust ultrathin shell of several nanometres through a simple, one-step, bubble-controlled, interfacial hydrolysis reaction. This material has exceptional properties, including ultralow density (0.028 g cm−3, approaching 99% porosity), good thermal stability up to 1000 °C, an exceptionally high capacity for oil uptake from mixed solvents (up to 25.6 cm3 g−1), and a very low thermal conductivity comparable to ultralow density silica aerogels.

Photothermocatalytic Synergetic Effect Leads to High Efficient Detoxification of Benzene on TiO2 and Pt/TiO2 Nanocomposite

Controlling the emission of volatile organic compound (VOCs) has become an important issue because they are not only hazardous to human health but also harmful to the environment. Among various VOCs, the carcinogenic and recalcitrant benzene, which is one of the most abundant aromatic hydrocarbons found in polluted urban atmospheres, has been regarded as a priority hazardous substance for which efficient treatment technologies are needed. Heterogeneous photocatalysis based on nanostructured TiO2 has attracted much research attention in the past decades as an important and promising technology for the detoxification of organic pollutants because of the superior photocatalytic activity, chemical stability, low cost, and nontoxicity of TiO2. However, when TiO2 photocatalysts are applied to the detoxification of benzene in the gas phase, they are prone to deactivation mainly due to the deposition of less reactive byproducts on the TiO2 surface, making the photocatalytic detoxification of benzene very inefficient. 4] Much effort has therefore been devoted to enhancing the efficiency of benzene photocatalytic oxidation. The modification of TiO2 with noble metal (e.g. , Rh and Pt) as co-catalysts has been found to boost the efficiency of benzene photocatalytic oxidation and improve the durability of TiO2 catalysts. Recently, photocatalytic oxidation combined with ozone oxidation on TiO2 has been developed to improve the efficiency of benzene or toluene oxidation. As ozone is also an air pollutant, additional setup was required to remove the its excess. Plasma-driven photocatalysis and catalysis have been reported to enhance VOC decomposition activity on TiO2 and Al2O3. [10] Developing a highly efficient and cost-effective strategy for the detoxification of recalcitrant VOCs, such as benzene, has been a great challenge. Herein, photocatalysis and thermal catalysis have been ideally combined together just by a facile method of coating TiO2 catalyst and Pt/TiO2 nanocomposite on the surfaces of a UV lamp without using any additional heater, by which both UV irradiation and nonradiative thermal energy emitted from the UV lamp are fully used, and the high efficient photothermocatalytic detoxification of benzene has been realized. In this perfect combination of photocatalysis and thermal catalysis, a new photothermocatalytic synergetic effect has been found for the first time. Various high-pressure Hg lamps have been widely used as UV light sources in photocatalytic studies for decades. However, their nonradiative thermal energy emitted has not been fully used. In the closed gas-phase reactor, when the selfrectified high-pressure Hg lamp was turned on, the thermal energy emitted from the lamp made its surface temperature automatically increase to 240 8C, which provided a possibility for photothermocatalytic oxidation to occur without using an additional heater. The TiO2 sample was coated on the surfaces of the lamp, and thus the TiO2 catalyst was co-excited by both UV irradiation and thermal energy. Under the photothermocatalytic condition, benzene was rapidly oxidized with time and